linux-kernel - Re: [PATCH] dma: pl330: Add support for DMA

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Message-ID: <53799D5B.2060001@metafoo.de>
Date:	Mon, 19 May 2014 07:57:47 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Tushar Behera <tushar.behera@...aro.org>
CC:	Jassi Brar <jassisinghbrar@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dmaengine@...r.kernel.org, Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Linux-ALSA <alsa-devel@...a-project.org>,
	Takashi Iwai <tiwai@...e.de>
Subject: Re: [PATCH] dma: pl330: Add support for DMA_PAUSE command

On 05/19/2014 05:10 AM, Tushar Behera wrote:
> On 16 May 2014 00:51, Lars-Peter Clausen <lars@...afoo.de> wrote:
>> On 05/15/2014 02:01 PM, Tushar Behera wrote:
>>>
>>> On 14 May 2014 17:54, Lars-Peter Clausen <lars@...afoo.de> wrote:
>>>>
>>>> On 05/14/2014 02:07 PM, Tushar Behera wrote:
>>>>>
>>>>>
>>>>> On 14 May 2014 17:29, Jassi Brar <jassisinghbrar@...il.com> wrote:
>>>>>>
>>>>>>
>>>>>> On Wed, May 14, 2014 at 8:53 AM, Tushar Behera
>>>>>> <tushar.behera@...aro.org>
>>>>>> wrote:
>>>>>>>
>>>>>>>
>>>>>>> While playing back audio, pmc_dmaengine requests the DMA channel to
>>>>>>> stop DMA transmission through DMA_PAUSE command.
>>>>>>>
>>>>>>> Currently PL330 driver doesn't support DMA pause command, leaving
>>>>>>> the DMA state inconsistent when the system resumes. Instead, it would
>>>>>>> be better to terminate the DMA transfer during suspend and restart
>>>>>>> again during resume.
>>>>>>>
>>>>>>> Tested with audio playback across a suspend-resume cycle.
>>>>>>>
>>>>>> What is pmc_dmaengine? How does DMA_PAUSE help, when there is no
>>>>>> DMA_RESUME?
>>>>>>
>>>>>
>>>>> Sorry, it is a typo.
>>>>>
>>>>> sound/core/pcm_dmaengine.c:snd_dmaengine_pcm_trigger() -->
>>>>> dmaengine_pause() is called during system suspend.
>>>>
>>>>
>>>>
>>>> It is only called if the DMA driver has support for pausing and resuming
>>>> DMA
>>>> transfers. Or at least that is the intention.
>>>>
>>>> - Lars
>>>
>>>
>>> During suspend, snd_dmaengine_pcm_trigger():SNDRV_PCM_TRIGGER_SUSPEND
>>> is called which unconditionally calls dmaengine_pause(). Should we
>>> update snd_dmaengine_pcm_trigger() to check for DMA pause/resume
>>> support and call dmaengine_pause() or dmaengine_terminate_all()
>>> accordingly?
>>
>>
>> As far as I understand it we do not have to do anything for TRIGGER_SUSPEND
>> if we do not set the SNDRV_PCM_INFO_RESUME flag. It looks like
>> TRIGGER_SUSPEND is called unconditionally during suspend. But since the
>> error code is ignored it should be fine if we just call dmaengine_pause()
>> and that return -ENOSYS or similar.
>>
>> Are you seeing an actual issue that you are trying to fix with your patch?
>>
>> - Lars
>>
>
> Without this patch applied, if audio is playing back while suspend is
> triggered, it doesn't playback after resume. Stopping the stream and
> replaying works.
>

Ok, I think your second suggestion was correct. Call 
dmaengine_terminate_all() instead of damengine_pause() in 
snd_dmaengine_pcm_trigger() if the dmaengine driver does not support pausing 
the transfer.

- Lars
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